The present invention generally relates to an ignition control apparatus for an internal combustion engine, and particularly relates to an ignition control apparatus for an internal combustion engine, in which an ignition timing and a current conduction initiating timing are controlled on the basis of a period of time elapsed from a reference position.
In an ignition control apparatus arranged to calculate an optimum ignition timing and an optimum current conduction initiating timing in accordance with the running state of an engine so as to determine an ignition timing and a current conduction initiating timing on the basis of time elapsed from a reference position, if the revolutional speed of an internal combustion engine is suddenly changed, the ignition timing is not controlled before the succeeding reference position signal is received to cause a delay in revolutional angle to thereby cause a delay in control to make the current conduction period of time insufficient, so that a miss burn may be caused and variations in ignition timing become larger. Consequently, it is necessary to detect the revolutional speed of the engine as quickly as possible, and it is preferable to make the time elapsed from the reference position for use for the determination of ignition timing shorter as much as possible. To this end, conventionally, as disclosed in a prior art reference, for example, Japanese Patent Unexamined Publication No. 84860/80, the time elapsed from a reference position has been made shorter by generating 24 pulses in one revolution (360 degrees) of a distributor. It is impossible, however, to detect a reference position of a crank, for example, a top dead center (a TDC) merely by the generation of those 24 pulses, and therefore it has been required to generate two TDC pulse signals for the discrimination of the reference position in addition to the 24 pulses in every revolution of the distributor. As described above, in the conventional technique, it has been necessary to provide two or more sensors revolved in synchronism with the revolution of the engine for accurately detecting the crank reference position, and therefore there has been such a disadvantage that the cost is increased correspondingly.